To estimate the relative risks of cancer in first-degree relatives of index patients, 130 pedigrees of dominantly inherited Lynch type II cancer family syndrome have been analysed. The risk of death from all causes was significantly increased in women over 45 years of age and the overall liability to cancer in women was greater than for men. A sevenfold increase in risk of colon cancer was found in both sexes. In female relatives the risk of breast cancer was increased fivefold and lifetime risk of breast cancer was 1 in 3.7. A screening programme based on estimated risks could be offered to first-degree relatives of index patients with Lynch type II cancer family syndrome.